There are a number of existing glass break sensors which use a microphone to detect the sound energy in a monitored space and process the signal to determine if a glass break event has occurred. Many of these detectors use technology which characterizes a glass break event as having an initial signal portion, commonly referred to as a "thud", which is associated with the initial impact between the striking object and the glass surface, followed by the formation and propagation of cracks in the glass, followed by the catastrophic destruction of the glass. After this initial portion, the glass fragments continue to resonate and strike other glass fragments as they hit the floor and surroundings. This latter portion is often referred to as a secondary effect or the "tinkle" portion.
It is also known for glass break detectors to detect an initial large amplitude component (i.e. the "thud") and then look for a latter portion of the signal having many high frequency components (the "tinkle"). These high frequency components would tend to indicate the shattering of glass.
Prior art detectors continue to have problems in distinguishing glass break events from non-glass break events. Common false alarms are caused by thunder, dropping metal objects, ringing of bells, service station bells, chirping birds, slamming doors, splintering wood and mouse traps. These sound sources typically have both low frequency components and high frequency components as would a glass break event. Many of these sounds are periodic in nature and, thus, are not random.
The detection arrangement according to the present invention provides improved accuracy in predicting that a glass break event has occurred and reduces problems with respect to false alarms. This accomplished in a relatively simple manner such that the cost of the sensor is relatively low.